The present application is based on and claims priority from PCT Application PCT/JP97/1778 filed on May 26, 1997 and Japanese Patent Application Hei 9-297882 filed on Oct. 14, 1997, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an AC generator for vehicles loaded on cars, trucks and the like.
2. Description of the Related Art
Recently, the engine and whole electric appliances of a vehicle are close to the road surface due to the slant nose of the vehicle. The slanted nose is designed for reducing the vehicle running resistance and improving the visibility. The water-splashing conditions caused by splashing water from tires during the running of the vehicle can be harsh. Further, in cold areas, a large amount of salts are scattered for the purpose of preventing the road from freezing during winter, and salt or water containing salt are dragged in during the running of the vehicle, resulting in harsher corrosive environment. Since the vehicular generator is exposed to the above-described environment, the generation of electrical energy may be stopped. As a result, when the vehicle stops, there is a danger of leaving people freezing to death in the cold weather.
The stoppage of the generation, in this case, is mainly caused by the fact that water is moved into the inner wall portion of the slot of the stator core thereby resulting in rust. The rust grows to reduce a sectional area of the slot, which changes after passage of time by which the conductors of the stator coil inserted into the slot is pressed to produce a short-circuit between the coils, resulting in a breakage of coil due to the burn loss of local heat generation. Further, even if insulating paper is provided to insulate between the slot and the coil, the insulating paper is sometimes broken due to the growth of rust and the rise in pressure of slot, resulting in a short-circuit between the electric conductors and stator. Furthermore, the movement of water into the slot of coil is repeated whereby the coil film leads to corrosion deterioration such as hydrolysis. This results in a short-circuit between the electric conductors. The repeated entry of water into the slot of the coil also leads to the burn loss of local heat generation and the elution of copper, finally resulting in a breakage of coil. This tendency is particularly problematic in the slot in which electric conductors of the coils are thickly present because during the step of inserting or after inserting the electric conductors into the slot of the stator coil, the insulating films on the surface of the electric conductors rub together to damage or locally reduce its thickness.
Further, in order to prevent the electric conductors of the coils, which are inserted into the slots, from projecting from the inlet of the slots, wedges made of insulating material are inserted between the electric conductors and the inlets of the slots. However, the insulation coating of the electric conductors may be harmed or thinned when inserting the wedges. Thus, in order to improve the durability, the protection of the surface of the insulation coating of the electric conductors while the stator is manufactured is very important.
In general, the coil ends are impregnated with thermosetting resin for insulation. The viscosity thereof is arranged to stay in the portions during the thermosetting period, and the resin does not flow into the slots. This does not insulate inner portions of the slots sufficiently to prevent the short circuit.
On the other hand, a slot of a stator coil can be coated with an insulating resin by means of electrode position coating or the like, and providing insulation paper for insulating between the slot and electric conductors of the coil is provided, as described in Japanese Patent Application Laid-Open No. Hei 1-278242. Further, a drip-proof cover is provided on the cooling air take-in side of a generator to cut off a direct water-splashing path from the outside, as described in Japanese Patent Application Laid-Open No. Hei 3-235644.
The method disclosed in Japanese Patent Application Laid-Open No. Hei 1-278242, provides no solution against the short-circuit between the electric conductors of coils due to the corrosion deterioration of the coil film in the slot. Further, the slot is narrowed by the thickness of the resin film and insulating paper to reduce the space for inserting the electric conductors of the coil by their thicknesses. This prohibits the increase of the thickness of the film of the coil to enhance the its corrosion resistance. Since the coating step is necessary, the production cost including material cost increases.
Further, in the method disclosed in Japanese Patent Application Laid-Open No. Hei 3-235644, teaches that in a recent small and high-output vehicular generator, a fan is provided on the side of a rotor. The rotation of the fan causes cooling air is taken into the generator. A stator coil is cooled by utilizing air discharged through a window provided diametrically of a frame, as shown in FIG. 10. That is, since the stator coil is positioned near the window for ventilation provided diametrically of the frame, water or salt water from the diametrical outside of the generator can easily reach the periphery of the stator. To prevent this, it is contemplated that a drip-proof cover is further mounted externally of the window provided diametrically of the frame. In this case, however, the ventilation resistance increases and the quantity of cooling air reduces, and an escape of hot air is impeded, thus posing a problem in that a temperature of the whole generator considerably rises. This addition of the drip-proof cover increases the production cost, similarly to the addition of the coating step as described above.
Further, JP-A-63-194543 discloses an electric conductor as shown in FIG. 11. The slots are generally rectangular in cross-section. The electric conductor has a portion inserted in a slot which generally has a generally rectangular cross section and a portion outside the slot which generally has a round cross-section. Thus, occupation ratio of the electric conductor in the slot becomes more than 80%. In other words, the ratio of the area in the gap is less than 20%. However, in this structure, a number of round conductors are stacked and formed to be rectangular. Therefore, the insulation coatings are harmed or the thinned due to rubbing or difference in the degree of deformation.
The present invention solves the above-described problems of prior art. An object of the present invention is to provide an AC generator for vehicles capable of preventing stoppage of generator due to a short-circuit within a stator slot caused by water-splashing from outside and which is excellent in terms of cost and does not pose new problems such as a rise in temperature or harm of the insulation coating of the electric conductors of the stator coil.
According to a first aspect of the present invention, a generator for a vehicle comprises a rotor having a fan on at least one side of both axial ends, a stator disposed oppositely of an outer periphery of the rotor, and a frame for supporting the rotor and the stator. The stator comprises a laminated core having a plurality of slots, a plurality of electric conductors of the stator coil housed in the slots, the electric conductors has generally the same cross sections inside and outside the slot and an insulator that provides electric insulation. There is a gap except the electric conductors and the insulator in a diametrical section of the slots, and an area ratio of the gap with respect to the sectional area of the slots is not more than 25%.
With this arrangement, even if water droplets containing salt or the like arrive at the neighborhood of an inlet of the slots of the stator core, the space gap for movement thereof into the slots is narrow. Thus, the water droplets remain on the external side of the stator core and do not flow into the space gap of the slots. This can prevent the generation of rust in the inner wall portion of the slots of the stator core and the corrosion deterioration of a coil film in the slots, thus preventing a short-circuit between the electric conductors of the coil and the stator core and between the electric conductors of the coils. Further, since the coating of inside of the slots and a drip-proof cover are not necessary, it is possible to reduce costs as compared with prior art. Moreover, when a polyamide resin and or a polyester resin are used for the film of the coil and the insulator, it is possible to prevent water droplets form moving into the space gap in the slots since these resins have a hydrophobic property. Further, because the above electric conductors have almost the same cross sections, harm or the thinning of the insulation coatings can be prevented.
According to the second aspect of the present invention, in the AC generator according to the first aspect, the width of the inlet of the slots is narrower than the minimum width of the electric conductors disposed in the slots, and there is only an insulator between the electric conductor and wall of the slot near the inlet. Thus, the electric conductors disposed in the inner periphery of the slots function to prevent other conductors in the slots from projecting from the inlet of the slots. Therefore, wedges can be omitted, so that harm or the thinning of the insulation coating during insertion of the wedges can be prevented and that short circuiting between the electric conductors or between conductors and the stator core due to water splashing can be prevented. Further, since the wedge can be omitted, the cost of parts and manufacturing can be reduced.
According to the third aspect of the present invention, the electric conductors according to the second aspect can be inserted along the slots so that the ratio of area in the gap can be reduced to less than 25%.
According to the fourth aspect of the invention, the electric conductors according to the first aspect of the invention disposed in the same slot are spaced apart from one another outside the slot. Therefore, there is no groove between the neighboring electric conductors, electrolyte such as salt water can not enter the inside of the slots guided by the groove. Thus according to the present invention, the electric conductors of the stator coils has the same cross sections both inside and outside the slots, and distance between the conductors in the slots is less than a certain value. Therefore, the stoppage of the generator caused by water-splashing from outside can be prevented. This is excellent in terms of cost.